A treatise on the geography and classification of animals / By William Swainson.

  • Swainson, William, 1789-1855.
Date:
1835
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on the geography and classification of animals / By William Swainson. Source: Wellcome Collection.

    366/390 (page 350)
    nomenclature of the “ Hore Entomologice” and the “‘ Northern Zoology,” are strictly sub-genera. They are not — each taken by itself — circular, because they have really but a few species; or, what is the same thing to the present question, we are only acquainted with a few species ; but, taken collectively, they form a cir- cular group, or, in other words, a genus, such as we have here defined. These are examples of sub-genera which are not in themselves circular ; but, from recent researches into the large and diversified assemblage of forms constituting the genus Papilio of Latreille, we feel thoroughly persuaded that, where there is a great numerical preponderance, sub-genera are not only circu- lar, but that they contain their own internal types, as definitely and perfectly as do genera and all higher groups. This latter question we shall probably inves- tigate in its proper place. In the mean time, having now enumerated all the ranks and degrees of circular groups yet detected, we shall proceed to make a few concluding observations upon species and their varieties. (431.) A Species, in the usual acceptation of the term, is an animal which, in a state of nature, is distinguished by certain peculiarities of form, size, colour, or other cir- cumstances, from another animal. It propagates, “ after its kind,” individuals perfectly resembling the parent: its peculiarities, therefore, are permanent. When ani-— mals are domesticated, the changes of life, of food, and frequently of country, which they undergo, are known to have the effect of altering and destroying those marks by which, ina state of nature, they were always distin- guished. We see this in all the domestic quadrupeds and birds, which, when under the dominion of man, diverge, as it were, into endless variety. The discrimination of species, in many instances, requires a very practised eye ; but where, on the other hand, there is an obvious difference in colour, size, markings, &c., the task be- comes easy. Sometimes all the species of a whole genus will be entirely black, as in the Drongo shrikes (Edolius), and in many of those composing the family